package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.util.PriorityQueue;

import java.text.Collator;
import java.util.Locale;

/**
 * Expert: Collects sorted results from Searchable's and collates them.
 * The elements put into this queue must be of type FieldDoc.
 *
 * <p>Created: Feb 11, 2004 2:04:21 PM
 *
 * @author  Tim Jones (Nacimiento Software)
 * @since   lucene 1.4
 * @version $Id: FieldDocSortedHitQueue.java 332431 2005-11-11 03:13:10Z yonik $
 */
class FieldDocSortedHitQueue extends PriorityQueue {

    // this cannot contain AUTO fields - any AUTO fields should
    // have been resolved by the time this class is used.
    volatile SortField[] fields;

    // used in the case where the fields are sorted by locale
    // based strings
    volatile Collator[] collators;

    /**
     * Creates a hit queue sorted by the given list of fields.
     * @param fields Field names, in priority order (highest priority first).
     * @param size  The number of hits to retain.  Must be greater than zero.
     */
    FieldDocSortedHitQueue(SortField[] fields, int size) {
        this.fields = fields;
        this.collators = hasCollators(fields);
        initialize(size);
    }

    /**
     * Allows redefinition of sort fields if they are <code>null</code>.
     * This is to handle the case using ParallelMultiSearcher where the
     * original list contains AUTO and we don't know the actual sort
     * type until the values come back.  The fields can only be set once.
     * This method is thread safe.
     * @param fields
     */
    synchronized void setFields(SortField[] fields) {
        if (this.fields == null) {
            this.fields = fields;
            this.collators = hasCollators(fields);
        }
    }

    /** Returns the fields being used to sort. */
    SortField[] getFields() {
        return fields;
    }

    /** Returns an array of collators, possibly <code>null</code>.  The collators
     * correspond to any SortFields which were given a specific locale.
     * @param fields Array of sort fields.
     * @return Array, possibly <code>null</code>.
     */
    private Collator[] hasCollators(final SortField[] fields) {
        if (fields == null)
            return null;
        Collator[] ret = new Collator[fields.length];
        for (int i = 0; i < fields.length; ++i) {
            Locale locale = fields[i].getLocale();
            if (locale != null)
                ret[i] = Collator.getInstance(locale);
        }
        return ret;
    }

    /**
     * Returns whether <code>a</code> is less relevant than <code>b</code>.
     * @param a ScoreDoc
     * @param b ScoreDoc
     * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
     */
    protected final boolean lessThan(final Object a, final Object b) {
        final FieldDoc docA = (FieldDoc) a;
        final FieldDoc docB = (FieldDoc) b;
        final int n = fields.length;
        int c = 0;
        for (int i = 0; i < n && c == 0; ++i) {
            final int type = fields[i].getType();
            switch (type) {
                case SortField.SCORE:
                    float r1 = ((Float) docA.fields[i]).floatValue();
                    float r2 = ((Float) docB.fields[i]).floatValue();
                    if (r1 > r2)
                        c = -1;
                    if (r1 < r2)
                        c = 1;
                    break;
                case SortField.DOC:
                case SortField.INT:
                    int i1 = ((Integer) docA.fields[i]).intValue();
                    int i2 = ((Integer) docB.fields[i]).intValue();
                    if (i1 < i2)
                        c = -1;
                    if (i1 > i2)
                        c = 1;
                    break;
                case SortField.STRING:
                    String s1 = (String) docA.fields[i];
                    String s2 = (String) docB.fields[i];
                    // null values need to be sorted first, because of how FieldCache.getStringIndex()
                    // works - in that routine, any documents without a value in the given field are
                    // put first.  If both are null, the next SortField is used
                    if (s1 == null)
                        c = (s2 == null) ? 0 : -1;
                    else if (s2 == null)
                        c = 1; // 
                    else if (fields[i].getLocale() == null) {
                        c = s1.compareTo(s2);
                    } else {
                        c = collators[i].compare(s1, s2);
                    }
                    break;
                case SortField.FLOAT:
                    float f1 = ((Float) docA.fields[i]).floatValue();
                    float f2 = ((Float) docB.fields[i]).floatValue();
                    if (f1 < f2)
                        c = -1;
                    if (f1 > f2)
                        c = 1;
                    break;
                case SortField.CUSTOM:
                    c = docA.fields[i].compareTo(docB.fields[i]);
                    break;
                case SortField.AUTO:
                    // we cannot handle this - even if we determine the type of object (Float or
                    // Integer), we don't necessarily know how to compare them (both SCORE and
                    // FLOAT contain floats, but are sorted opposite of each other). Before
                    // we get here, each AUTO should have been replaced with its actual value.
                    throw new RuntimeException("FieldDocSortedHitQueue cannot use an AUTO SortField");
                default:
                    throw new RuntimeException("invalid SortField type: " + type);
            }
            if (fields[i].getReverse()) {
                c = -c;
            }
        }

        // avoid random sort order that could lead to duplicates (bug #31241):
        if (c == 0)
            return docA.doc > docB.doc;

        return c > 0;
    }
}
